The present invention is directed to a composition and method for reducing residue and scum formation originating from photolithographic compositions as well as reducing foam formation. More specifically, the present invention is directed to a composition and method for reducing residue and scum formation originating from photolithographic compositions and for reducing foaming with a diphenyl oxide compound in combination with an antifoam agent.
Residue and scum from photolithographic compositions such as photoresists, surfactants, alkaline compounds and antifoam agents from developer and stripping compositions present difficult cleaning problems for the electronics industry. Such residue and scum can build-up on various products and apparatus. Photoresist materials are employed in the manufacturing of semiconductor devices, and electronic components such as integrated circuits, photomasks for the manufacture of integrated circuits, printed wiring boards and the like as well as planographic printing plates. In photolithographic processing, a step in the process of making electronic devices and components, a substrate surface is coated with a photoresist, i.e., a coating composition that is sensitive to actinic radiation, e.g., ultraviolet light, X-rays, electron beams and the like, to give a layer that is sensitive to actinic radiation which is irradiated pattern-wise with the actinic radiation. The irradiated photoresist is then developed with a developer solution to form a patterned photoresist layer that serves to selectively protect the substrate surface from etching, plating or diffusion of dopants.
Photoresists may be positive-working, or negative-working. Such photoresists may be liquid, or dry film. A photoresist composition of the positive-working type has such a photosensitivity that solubility of the composition in the developer solution is increased by exposure to light so that the patterned photoresist layer is formed on the areas unexposed to ultraviolet light where the composition is left undissolved. A negative-working photoresist composition exhibits behavior of a sensitivity and solubility that is the reverse of the positive-working photoresist.
Along with recent progress in the technology of semiconductor devices with a requirement for finer and finer high-fidelity patterning of a line width of 1 micron or even finer to comply with the trend of increased density of integration in semiconductor devices, photolithographic processes of patterning using a positive-working photoresist also envisages a difficult problem. When patterning is desired of an extremely fine contact hole in a fine pattern, alkaline developer solution is admixed with a surface active agent with an object to increase the wettability of the substrate surface with the aqueous developer solution. One of the problems in the addition of a surface active agent to the developer solution is that film residues and scums sometimes occur on the exposed areas where the photoresist layer desirably is dissolved away completely and cleanly. Although the film residues and scums can be removed by gently treating the surface with oxygen plasma or sputtering, no complete solution of the problem can be obtained by such methods because such treatments must be performed under well controlled troublesome conditions and is not efficient in respect of smooth removal of the scums, or gives no uniform effect of treatment in finely patterned areas having contact holes of about 1 micron or smaller in diameter.
U.S. Pat. No. 4,820,621 to Tanaka et al. has addressed the problem of residue and scum formation by modifying a developer solution with the addition of a non-ionic surface active agent that is a polyoxyethylene alkyl-substituted phenyl ether. The ether is included in the developer solution in an amount of from 50 to 5000 ppm (parts per million). The developer solution is employed in patterning using a positive-working photoresist composition composed of an alkali-soluble novolac resin and a naphthoquinone diazide compound. The '621 patent alleges that patterning the positive photoresist with the developer containing the polyoxyethylene alkyl-substituted phenyl ether prevents formation of residues and scums after development.
Similar residue and scum formation also occur when negative-working photoresists are employed. For example, in manufacturing printed circuit boards UV curable negative-working photoresists may be used. Exposed portions of the photoresist become insoluble in alkaline developer solution and form a protective barrier to other processing chemicals such as etching and plating solutions. Unexposed portions of the photoresist are to rinse freely from the circuit board with an alkaline solution such as a 1% sodium carbonate, monohydrate in water. Development occurs because polymers in the photoresist contain acid functionality. Such acid functionality within the polymers are neutralized in alkaline solution forming a water soluble organic salt. As the dissolved photoresist builds up in solution (developer loading), insoluble organic materials begin to form in the developing tank eventually forming a water insoluble residue or scum. Presence of anti-foam additives (conventionally added to developing solutions to minimize foaming) greatly increases the tendency for residue and scum to form. As the level of scum builds, chances increase for an inadvertent redeposit of these water insoluble residues onto the developed circuit board. Such redeposited residues cause a retardation of the etching solution (etching chemistries have difficulty penetrating any organic residues). Where etch is retarded, circuit shorts form causing a defective circuit board. In addition to increasing the potential for defective circuit boards, the residue also makes cleaning equipment difficult, thus increasing maintenance time.
In addition to the problem of built-up residue and scum formation from primary photoresists, there also is a residue and scum build-up problem from secondary photoresists. Such secondary photoresists may be employed in soldermasks. Residue and scum are deposited on a substrate as a result of component separation in the soldermask. Such component separation may be exacerbated when an improperly balanced soldermask developer solution, i.e., improper developing conditions and/or soldermask developer solution chemistry, contact the soldermask. Built-up residue and scum from secondary photoresists often appear as a bright green coating on a substrate such as a developer apparatus.
Conventional cleaners used to remove residue and scum may vary in composition. Typically, such conventional cleaners include as active ingredients a strong base such as sodium hydroxide, and chelating agents such as ethylene diamine tetraacetate (EDTA). Surfactants, solvents and emulsifying agents may also be included in the cleaners. Conventional cleaners are employed at temperature ranges from about 45° C. to about 55° C. Such conventional cleaners are primarily used because of the low cost of their ingredients. However, workers in the field using such conventional cleaners have discovered that the residue problem is often made worse. Often the equipment has to be manually cleaned to remove the residue from the photoresist as well as the conventional cleaners. Such manual cleaning is both a labor and time intensive operation that can cause a significant loss of production time. Further, as mentioned above, such cleaners are not effective enough for removing residue from new generation photoresists that have many hydrophobic aromatic materials. Accordingly, it is advantageous to reduce or prevent the build-up of such residue and scum to prevent or at least reduce the amount of cleaning.
U.S. Pat. No. 5,922,522 to Barr et al.; U.S. Pat. No. 6,063,550 to Lundy et al.; and U.S. Pat. No. 6,248,506 B1 to Lundy et al. disclose surfactant and surfactant mixtures included in developer solutions that prevent or inhibit the formation of residues and scum on circuit boards and circuit board manufacturing equipment. Such surfactants are composed of a hydrophobic group, an alkoxylated hydrophilic group and a nonionic or anionic capping group. Examples of suitable hydrophobic groups include nonylphenol, octylphenol and tristyrylphenol. Examples of suitable alkoxylated hydrophilic groups include ethylene oxide, propylene oxide and ethylene oxide/propylene oxide groups. Examples of suitable capping groups include hydroxyl, carboxyl, sulfonyl, phosphonyl, or mixtures thereof. Such residue and scum reducing compounds are included in developer solutions in amounts of from about 0.05% to about 1.0% by weight.
Although the developer solutions disclosed in U.S. Pat. Nos. 5,922,522; 6,063,550; and 6,248,506 B1 provide an effective means of reducing the amount of build-up of residue and scum on substrates containing photoresist, such as circuit boards, and equipment used in the manufacture of electronic components, there is still a need for a composition and method for further reducing the amount of residue and scum formation to reduce cleaning or to prevent cleaning. Additionally, there is also a need for a cleaning composition and method for further reducing foam formation in both developer and stripper solutions. While the above-mentioned patents address residue and scum formation in developer solutions, the patents do not address the problem of residue formation or foam formation in stripper solutions. Thus, there is a need for a composition that prevents residue formation and foaming in both developer and stripper solutions. Developers may be acid or basic solutions that remove un-cross-linked photoresist from a substrate after exposure of the photoresist to actinic radiation. Strippers are acidic or basic solutions that remove all photoresist from a substrate.
Photoresist that is removed by developer and stripper solutions can cause undesirable amounts of foaming. If the foaming is excessive, it can overflow from apparatus, and cause the solution levels to go down below a minimum threshold level that may result in equipment shutdown. Foaming can also obscure the field of view of workers making it difficult to determine photoresist break points, and to monitor panels in developing chambers. It is also more difficult to clean equipment that contains significant amounts of foam. Washing with water only aggravates the foaming problem In many cases, antifoaming agents are utilized in developing and stripping baths.
Many commercially available antifoams, however, can increase the amount of undesirable residue in developer and stripping solutions. The solutions can contain fairly high levels of organic material because the developed or stripped photoresist are emulsified and/or solubilized in the solution. An analysis of the residue from such photolithographic compositions reveals that it is a complex mixture of photoresist, antifoam, developer or stripper components. These residues can float on a developer or stripper solution surface and/or adhere to equipment parts. As mentioned above, presence of these residues can cause sub-optimum performance of the process equipment and surface contamination of the circuit boards. Both of these factors can result in printed wiring board defects. As a result, the key requirements for an antifoam in a developer or stripper are to control foaming in addition to minimizing the formation of residues from photolithographic compositions.
Accordingly, it is advantageous to have an antifoam product that effectively lessens the amount of foam while also reducing undesirable residues in photoresist developers. It is useful if the same antifoam product minimizes the foaming in photoresist strippers. Many antifoams are not suitable for both developers and strippers. Thus, there is a need for a composition that reduces or inhibits residue and scum deposited by photolithographic compositions, and reduces or inhibits foaming.